Various methods and devices have been described for determining the position of a probe or catheter tip inside the body using electromagnetic fields, such as in U.S. Pat. No. 5,391,199 to Ben-Haim, European Patent 0 776 176 to Ben-Haim et al., U.S. Pat. Nos. 5,833,608 and 6,161,032 to Acker, and U.S. Pat. Nos. 5,558,091 and 5,752,513 to Acker et al., all of which are assigned to the assignee of the present patent application and are incorporated herein by reference. U.S. Pat. No. 5,913,820 to Bladen et al. and U.S. Pat. No. 5,042,486 to Pfeiler et al., both of which are incorporated herein by reference, also describe electromagnetic position-determination systems. Other electromagnetic tracking systems, not necessarily for medical applications, are described in U.S. Pat. No. 3,644,825 to Davis, Jr. et al., U.S. Pat. Nos. 3,868,565 and 4,017,858 to Kuipers, U.S. Pat. No. 4,054,881 to Raab, and U.S. Pat. No. 4,849,692 to Blood, which are likewise incorporated herein by reference.
Because of manufacturing variations, the coils generally used in the position sensors of these position-determining systems to generate position signals may not be precisely oriented with the body of the probe. Additionally, the distance of the coils from the tip of the probe may not be precisely known, and there may be slight variations in the relative gains of the coils in response to externally-applied fields. U.S. Pat. No. 6,266,551 to Osadchy et al., which is assigned to the assignee of the present patent application and is incorporated herein by reference, describes methods and apparatus for pre-calibrating a probe, preferably at the time of manufacture, so as to measure and compensate for variations in the positions, orientations and gains of the coils. To calibrate the probe, a mechanical jig holds the probe in one or more predetermined positions and orientations, and radiators generate known, substantially uniform magnetic fields in the vicinity of the jig. Signals generated by the coils are analyzed and used to produce calibration data regarding the gains of the coils and deviations of the coils from orthogonality.
Various methods and devices have been described for storing, in a probe, information specific to the probe, such as calibration and identification information. These devices generally include a microchip incorporated in the probe. For example, the above-cited U.S. Pat. No. 6,266,551 to Osadchy et al. describes the incorporation of an electronic microcircuit in a probe, which stores information relating to calibration of the probe. Such information can include an encrypted calibration code and/or a usage code, which controls availability of the probe to a user thereof.
U.S. Pat. No. 6,370,411 to Osadchy et al., which is assigned to the assignee of the present patent application and is incorporated herein by reference, describes a catheter assembly comprising a catheter of minimal complexity and a connection cable which connects the proximal end of the catheter to a console. The catheter comprises a microcircuit which carries substantially only information specific to the catheter, such as calibration data, which is not in common with other catheters of the same model. The cable comprises an access circuit which receives the information from the catheter and passes it in a suitable form to the console.
U.S. Pat. No. 6,248,083 to Smith et al., which is incorporated herein by reference, describes a guide wire assembly having a measuring device mounted in the distal end portion thereof. It also has an interface cable which includes information storage, containing calibration/temperature compensation data, uniquely characteristic of the measuring device. The calibration data is used with uncompensated output from the measuring device to calculate a correct measurement value.
U.S. Pat. No. 6,112,113 to Van Der Brug et al., which is incorporated herein by reference, describes an image-guided surgery system that includes a position measuring system for measuring a position of an instrument. The image-guided surgery system includes a test system which is arranged to measure the instrument, using the position measuring system, by measuring a calibration position of a reference part of the instrument while an object part of the instrument is situated in a calibration location or in a test position.
U.S. Pat. No. 6,335,617 to Osadchy et al., which is assigned to the assignee of the present patent application and is incorporated herein by reference, describes a method for calibrating a magnetic field generator. According to the method, magnetic field sensors are affixed to a probe in known positions and orientations, and one or more known locations in the vicinity of the magnetic field generator are selected. The magnetic field generator is driven so as to generate a magnetic field. The probe is moved in a predetermined, known orientation to each of the locations, and signals are received from the sensors at each of the locations. The signals are processed to measure the amplitude and direction of the magnetic field, at the respective positions of the sensors, and to determine calibration factors relating to the amplitude and direction of the magnetic field in the vicinity of the magnetic field generator.
U.S. Pat. No. 4,567,896 to Barnea et al., which is incorporated herein by reference, describes a sector-scan ultrasonic imaging apparatus having a biopsy attachment for positioning a biopsy needle relative to the ultrasonic scan head of the imaging apparatus. The biopsy needle is calibrated with a scan head coordinate system which defines a sector sweep of the scan head by determining the coordinates of the needle in the scan head coordinate system independently of determining the particular spatial relationship of the needle in operative position relative to the scan head. A calibration member adapted to be mounted on the biopsy attachment includes at least two ultrasonic reflection regions which are scanned by the scan head during the calibration mode and displayed on an image display device. The display of these reflection regions enables the needle coordinates to be determined using the predetermined geometric relationship of the calibration member with respect to the imaging apparatus housing.